The invention relates to a method and device for operating an internal combustion.
A method for operating an internal combustion engine and a device including at least one cylinder are conventional; in that context the ignition angle in the at least one cylinder is displaced from the engine-speed-dependent or load-dependent basic ignition angle on the basis of utilization of a knock control system. The adjustment angle depends on the frequency of knocking in the at least one cylinder, and is greater, the more frequently the knock signal has occurred in the previous working cycles.
The method according to the present invention and the device according to the present invention may provide, in contrast, the advantage that the reduction in torque caused by the ignition retard resulting from the knocking may be decreased. It may be possible to advance the ignition angle once again and thus achieve greater torque, and thereby increase the output of the internal combustion engine. Better efficiency may thus be achieved.
One action in the case of a direct gasoline injection internal combustion engine, in order to advance the ignition angle, may be to perform a double injection operation in one working cycle of a cylinder. By manner of a first injection, a lean basic mixture may first be formed in the respective cylinder, into which injection then occurs a second time. The lean basic mixture that may still be present in peripheral zones of the mixture even after the second injection reduces the knock susceptibility. In addition, the fuel delivered to the combustion chamber by the second injection cools the fuel/air mixture, which results in a further reduction in knock susceptibility. It may be advantageous, when a double injection is used, not to modify the volume of fuel to be injected as compared to a single injection, so that less fuel may be consumed in terms of the achievable output. An additional feature may be to a change in the exhaust gas recirculation rate, if an exhaust gas recirculation system is used in the internal combustion engine. At a higher exhaust gas recirculation rate, the knock susceptibility may also be reduced because of a decrease in the oxygen content of the fuel/air mixture.
It may be advantageous to employ as the representative adjustment angle the mean of all individual-cylinder retard angles of the cylinders, since an error-prone switchover may thereby be prevented. On the other hand, however, it also may be advantageous to employ the individual-cylinder retard angles as adjustment angles, and to carry out activation of the knock prevention operating mode in individual-cylinder fashion, so that a very accurate reaction to the individual cylinders"" properties may take place.
It may be advantageous to carry out the knock prevention with double injection operating mode only above a definable first load threshold, since application of the knock prevention with double injection operating mode may be desirable only in a specific load range. Upon switching back into another operating mode when the load falls below a specific threshold value, it may be desirable to select that second load threshold value in such a manner that it lies below the first load threshold value, in order to prevent an unstable state and continual switching back and forth between two operating modes. Since both the first load threshold value and the second load threshold value may be different depending on the engine speed, it may be desirable to take this engine speed dependence into account.
For the knock prevention with exhaust gas recirculation operating mode as an additional action reducing the knock susceptibility, it may be desirable to access this only below a definable third load threshold value, since the exhaust gas recirculation feature yields no torque gain at higher loads. By analogy with the knock prevention with double injection operating mode, the intention is to eliminate unstable states between two operating modes, so that advantageously the fourth load threshold value, at which operation may be switched back from the knock prevention with exhaust gas recirculation operating mode into another operating mode, should lie above the second load threshold value. Since both the third load threshold value and the fourth load threshold value may be different depending on the engine speed, it may be desirable to take this engine speed dependency into account, by analogy with the knock prevention with double injection mode.
It may be advantageous, upon activation of the knock prevention operating mode, also to take as the basis for the basic ignition angle another load-dependent and/or engine-speed-dependent characteristics diagram specific to that operating mode, since the conditions in the combustion chamber and thus the ignitability of the fuel/air mixture have been greatly changed by the additional action.